Rinnai Concentric Venting
Rinnai tankless water heaters use a single tube for their venting, how do they do this? It’s quite a simple process that prevents two holes from being drilled in your wall. As you can see in the picture of the elbow, the vent pipe has two distinct sections. This type of venting piping is called concentric venting. The tankless concentric vent pipe handles both the incoming supply air as well as ejecting the toxic exhaust gases. This form of tankless venting can save an extra hole in your wall and thus reduced risk of air leakage.
Concentric venting is really quite expensive as the pipe is made from stainless steel. On average you are looking at about 60 dollars per foot plus installation. This is why it important to position a Rinnai tankless water heater as close as possible to its venting termination point.